This invention relates to superconductors in general and more particularly to a superconductor structure with at least one inner, ribbon-shaped superconductor which is stabilized by a normally conducting material and is surrounded by a jacket which consists of a material of higher mechanical strength than the normally conducting stabilizing material and the interior of which is provided with cavities for conducting a cooling medium in the lengthwise direction of the conductor and to a method for manufacturing such a superconductor structure.
To generate strong magnetic fields of large physical dimensions, magnet windings with superconductors can be used to advantage. Examples of conductor materials useful for this purpose include, for instance, niobium-zirconium or niobium-titanium alloys as well as niobium-tin compounds. Conductors of these superconductive materials are generally stabilized with normally conducting material; for instance, they are stabilized by embedding them in a matrix of this material. This measure aids in preventing destruction of the superconductors in the event of an uncontrollable transition of their portions consisting of the superconductive material from the superconducting to the normally conducting state. When the superconductors are cooled by means of a coolant, generally by means of liquid helium, to a temperature below the so-called critical temperature of the superconductor used for the conductors, their ohmic resistance almost completely disappears. Because of the correspondingly reduced power requirement, superconductor magnets therefore have the advantage, over conventional magnets with windings of electrically normally conducting material such as, for instance, copper, that stronger magnetic fields, and, therefore, also higher magnetic field gradients can be obtained with them. Such superconducting magnet windings are advantageously suited for fusion reactors, the strong magnetic fields of which are used to hold a hot plasma together by means of magnetic forces and to thereby make possible a fusion process in the plasma. In addition, corresponding superconducting windings can also be used for deflecting or focussing charged particles, for instance, in particle accelerators.
The windings of such superconducting magnets must often be constructed from several winding layers. The superconductors are subjected, depending on the current loading and the number of turns of the magnets, to tensile forces in the lengthwise direction of the conductors and to compression forces at right angles to the conductor axis. The superconductors must be able to absorb these factors without danger that their portions consisting of superconductive material might get damaged due to deformation. In addition, such conductors must be protected especially against mechanical instabilities which are caused by conductor movements, since these instabilities can lead to a warming of the conductors causing them to go into a normally conducting state.
To take up such forces, the superconductors, which are generally ribbon shaped, can each be surrounded by a jacket which consists of reinforcement material which has a higher mechanical strength than the normally conducting stabilizing material. A superconductor design of this kind is disclosed in German Offenlegungsschrift No. 26 02 734. In a magnet winding, such a superconductor structure can then be directly braced against the superconductor structure adjacent to it using these jackets. While large forces can be transmitted with this bracing method, there is generally no space between adjacent jackets for conducting the coolant which is necessary for cooling the superconductor. In addition, the thermal conductivity of the reinforcement material of the jackets, generally, is also less than that of the stabilizing material of the superconductors. In the known superconductor structure, the interior enclosed by the jacket, in which the superconductor itself is also arranged, therefore contains several additional cavities which are used for conducting a coolant in the lengthwise direction of the conductor.
The known superconductor structure is manufactured by arranging a ribbon shaped superconductor, which contains a normally conducting matrix material, for instance, of copper, in which individual superconducting strands are embedded, in a corresponding recess between two support parts, likewise of normally conducting material, for instance, the matrix material, which are to be put together. The two support parts thereby form a body of normally conducting material, in which the superconductor proper is enclosed. In addition, cavities serving as cooling ducts are provided in the body formed by the support parts. After the two support parts are joined together, for instance, by welding, to form the body, they are additionally completely enclosed on their outside by a jacket of sheet steel. For this purpose, a metal sheet is bent around the common body formed by the two support parts and is welded together at its longitudinal sides abutting in the lengthwise direction of the conductor. However, the manufacture of such a superconductor structure is relatively expensive, paticularly because of the required support parts.